I have several instances of httpd running on my Mac. Don't need to run a web server, would like to end them all, as they add up to about 100mb of unnessecary RAM. What is the configuration that sets them to run? How can I disable it?

Fair, but in the future as more users come back to this same question they may be on 10.8 (or later) so overtime this is a more relevant answer.
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JeffOct 12 '12 at 20:29

This solved it for me on 10.7.5; even though Web Sharing exists and is unchecked in System Preferences, httpd was surviving/respawning through killall until using this launchctl command (but this particular system might have other issues)
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rymoJun 13 '13 at 18:50

So why the downvote? This method works... not something hard.You can just google this
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GutsygibbonOct 12 '12 at 19:05

httpd is normally started by /System/Library/LaunchDaemons/org.apache.httpd.plist, and changing the contents of /System is not recommended. Using launchctl to manage it (as @Jeff recommended) is a much better way to do it.
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Gordon DavissonOct 13 '12 at 14:25